Current hard drives use a Contact Start-Stop (CSS) system allowing a magnetic head, used to read and write data, to contact the surface of a magnetic disk in a specific CSS region when the disk is stationary. Thus, before the rotation of the spinning disk has stopped, the magnetic head is moved to the CSS region, where the magnetic head strikes on the surface of the disk. When the disk again starts to rotate, the magnetic head slides along the disk surface in this region, until the laminar airflow at the disk surface, caused by its rotation, fully lifts the magnetic head from the disk surface.
After the magnetic head is lifted in this way, it is moved from the CSS region to another region of the disk to read and write data. The CSS region is preferably textured to minimize physical contact between the magnetic head and the disk surface. In this way, the contact stick-slip phenomenon often called "stiction" and other frictional effects are minimized, along with the resulting wear of the magnetic head surface. Outside the CSS region, the remainder of the disk surface preferably retains a specular smoothness by avoiding physical contact with the magnetic head, permitting the reading and recording of high-density magnetic data.
U.S. Pat. No. 5,658,475 describes a laser tool for texturing disks to be used in hard disk drives in computer systems. The process leaves an annular textured portion of both sides of each disk. Disks are moved into and out of the texturing process in cassettes, through two disk-handling stations. In each disk-handling station, a lifter raises each individual disk from the cassette in which it is carried. The individual disk is then transferred to a pick-and-place mechanism, which moves it to a spindle. The spindle spins and translates the disk, so that both sides of the disk are exposed to beams derived from a pulsed laser. The pick-and-place mechanism then returns the disk to the lifter, which lowers it into the cassette pocket from which it was taken. The-pick-and place mechanism simultaneously moves one disk from the lifter to the spindle and another from the spindle to the lifter. While disks are moved by the pick-and-place mechanism of one disk handling station, a disk in the spindle of the other disk handling station is exposed to the laser beams.
The texturing process uses, for example, a tightly-focused, Q-switched, diode-pumped Nd:YLF solid state laser, providing an output at an infrared wavelength of 1047 nanometers, or an ND:YVO.sub.4 solid state laser. The beam from the laser is broken into two sub-beams within a beamsplitter, with one of the sub-beams being directed to a first side of the disk being textured, and with the other sub-beam being directed to the second (other) side of the disk being textured. With this system, each pulse of the texturing laser, traveling as the two sub-beams, produces a single textured spot on each side of the disk being textured. Depending on the adjustment of various parameters, each textured spot may be a depression, a depression with a surrounding raised ridge, or a bump surrounded by a trough, which is in turn surrounded by a raised ridge.
Recent developments in the design of hard disk drives lead to a reduction in size of the magnetic head used for reading and writing data, and hence to a need for smaller patterns of textured spots placed more closely to one another. To make smaller textured spots, the size of the laser spot directed at the disk must be reduced. In an optical system for laser texturing, the laser beam is focused onto the disk through a lens having an aperture which controls the laser spot size. The laser spot size is directly proportional to the wavelength of the laser beam and inversely proportional to the diameter of the focusing lens aperture. On the other hand, simply reducing the aperture diameter may reduce the depth of focus to the optical system to a point at which it becomes difficult to produce consistently-shaped textured spots. The depth of focus of the system is directly proportional to the wavelength and inversely proportional to the square of the aperture diameter. Thus, if the wavelength is reduced by 50 percent, the aperture size must be increased by about 40 percent to maintain the same depth of field. However, even with this increase in aperture size, the spot size is still reduced to about 70 percent of the spot size produced with the longer wavelength. Thus, what is needed is a system using a texturing laser having a wavelength of about half that of the infrared laser (1047 nanometers). Such a system may use, for example, a green laser having a wavelength of 532 nanometers.
Since these spots must be placed more closely together in a circumferential direction, the texturing laser beam must be pulsed more rapidly, assuming that the rotational speed of the disk being textured is not changed. Since these spots must be placed more closely together in a radial direction, more revolutions of the disk must occur while the annular portion of the disk is textured. In order to maintain a satisfactory level of throughput in a production environment, the rotational speed of the disk must be increased, again causing an increase in the rate at which the texturing laser beam is pulsed.
The pulsed laser technology U.S. Pat. No. 5,658,475 is limited to operation at about 100,000 pulses per second. Operation at higher speeds does not allow time for sufficient energy to build up within the laser cavity before a pulse is to be emitted. What is needed is apparatus operable at a much higher rate to provide smaller textured spots in an efficient manner.
As the rate at which the texturing laser beam is pulsed is increased, the times required to turn this beam on and off can become significant portions of the time during which texturing occurs, depending on the type of beam modulation used. That is, the texturing laser beam is only partly turned on during significant portions of the process used to form a single textured spot. This time-varying laser geometry can result in an unevenly formed textured spot. Furthermore, as the rotational speed of the disk being textured is increased, the surface of the disk moves through an increased distance during the exposure of a spot to a laser pulse. This effect can also result in an unevenly formed textured spot. Thus, what is needed is a method for forming an evenly shaped textured spot by exposing the moving disk surface to a time-varying laser geometry.